During the use of household equipment, insulation deterioration of equipment or erroneous wiring of power supply may cause the outer surface of equipment energized; if a person contacts the surface then a current will flow though the person's body to the earth and cause the causalities. Connecting a ground wire with the equipment or using a conductor to connect the equipment to the earth directly can pass the leakage current directly to the earth and prevent the causalities. However, in many cases the outer surface of equipment is not well grounded.